Hydraulic valve lifters have been utilized for some time so as to vary timing and duration of valve opening so as to provide more optimum engine performance at various operating conditions. One such system employing hydraulic valve lifters is disclosed in U.S. Pat. No. 4,615,306 entitled "Engine Valve Timing Control System" of Russell J. Wakeman, issued Oct. 7, 1986 (the entire contents of this prior patent being expressly incorporated hereinto by reference and referred to hereinbelow as "the Wakeman '306 patent"). In the Wakeman '306 patent, valve timing and valve opening duration are controlled via pressure pulses developed within the engine oil supply as a result of lifter operation. The valve lifters themselves include a collapsible hydraulic link controlled by a solenoid.
In a particular embodiment (see FIG. 6 of the Wakeman '306 patent), a pair of pistons defines therebetween a chamber which communicates with the solenoid. As the lower piston is being moved up the cam's profile, oil is pushed out of the lifter into bleed passageways until the lower piston's displacement is to be hydraulically transferred to the upper piston as dictated by an electronic control unit (ECU), at which time the solenoid is energized thereby forming a solid hydraulic link coupling the motion of the lower piston to the upper piston which, in turn, actuates valve opening.
By means of the present invention, modular, self-contained hydraulic valve timing systems are provided which embody the beneficial functions of the Wakeman '306 patent. Specifically, cast valve covers according to this invention are provided with a solenoid valve, hydraulic valve lifters, and internal hydraulic passageways which fluid connect the solenoid valves and valve lifters.
Hence, according the the present invention, the hydraulic circuitry for the valve timing system is self-contained within an integral enclosure (i.e., the valve cover) so that during engine production, the valve cover may simply be coupled to the engine block with the electrical leads from the engine control unit (ECU) then being connected to the solenoid valve. As may be appreciated, these modular hydraulic valve timing systems of the present invention may be used by original equipment manufacturers (OEM's) in their original production engines, or may be employed to "retrofit" existing engines to provide them with variable valve timing capabilities.
These, and other, advantages and aspects of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.